WO2014133092A1 - 組換え酵母を用いたエタノールの製造方法 - Google Patents
組換え酵母を用いたエタノールの製造方法 Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
- C12P—FERMENTATION OR ENZYME-USING PROCESSES TO SYNTHESISE A DESIRED CHEMICAL COMPOUND OR COMPOSITION OR TO SEPARATE OPTICAL ISOMERS FROM A RACEMIC MIXTURE
- C12P7/00—Preparation of oxygen-containing organic compounds
- C12P7/02—Preparation of oxygen-containing organic compounds containing a hydroxy group
- C12P7/04—Preparation of oxygen-containing organic compounds containing a hydroxy group acyclic
- C12P7/06—Ethanol, i.e. non-beverage
- C12P7/08—Ethanol, i.e. non-beverage produced as by-product or from waste or cellulosic material substrate
- C12P7/10—Ethanol, i.e. non-beverage produced as by-product or from waste or cellulosic material substrate substrate containing cellulosic material
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- C12N1/00—Microorganisms, e.g. protozoa; Compositions thereof; Processes of propagating, maintaining or preserving microorganisms or compositions thereof; Processes of preparing or isolating a composition containing a microorganism; Culture media therefor
- C12N1/14—Fungi; Culture media therefor
- C12N1/16—Yeasts; Culture media therefor
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- C12N9/00—Enzymes; Proenzymes; Compositions thereof; Processes for preparing, activating, inhibiting, separating or purifying enzymes
- C12N9/0004—Oxidoreductases (1.)
- C12N9/0008—Oxidoreductases (1.) acting on the aldehyde or oxo group of donors (1.2)
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- C12N9/00—Enzymes; Proenzymes; Compositions thereof; Processes for preparing, activating, inhibiting, separating or purifying enzymes
- C12N9/90—Isomerases (5.)
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E50/00—Technologies for the production of fuel of non-fossil origin
- Y02E50/10—Biofuels, e.g. bio-diesel
Definitions
- the present invention relates to a method for producing ethanol using recombinant yeast having xylose metabolism ability.
- Patent Document 1 discloses a yeast in which a xylose reductase gene and a xylitol dehydrogenase gene derived from Pichia stipitis and a xylulokinase gene derived from S. cerevisiae are integrated into a chromosome.
- Non-patent Documents 1 and 2 disclose that acetic acid is contained in a large amount of hydrolyzate of cellulosic biomass and inhibits yeast ethanol fermentation.
- yeast introduced with a xylose utilization gene significantly inhibits ethanol fermentation using xylose as a sugar source (Non-patent Documents 1 and 2).
- moromi fermented saccharified cellulosic biomass with cellulase mainly contains unfermented residues, difficult-to-ferment residues, enzymes and fermentation microorganisms.
- the reaction liquid containing moromi for the subsequent fermentation the fermentation microorganisms can be reused, the amount of new input microorganisms for fermentation can be reduced, and the cost can be reduced.
- acetic acid contained in the moromi is also brought in at the same time. As a result, the concentration of acetic acid contained in the fermentation medium increases, which may inhibit ethanol fermentation.
- acetic acid As another method for avoiding fermentation inhibition by acetic acid, it is conceivable to metabolize acetic acid in the medium simultaneously with ethanol fermentation.
- the metabolism of acetic acid is an aerobic reaction and overlaps with the metabolic pathway of ethanol. Therefore, when fermentation is performed under aerobic conditions, acetic acid may be metabolized, but at the same time, the target substance ethanol is also metabolized.
- the glycerol production pathway by the GPD1 and GPD2 genes is a pathway that oxidizes surplus coenzyme NADH generated in metabolism to NAD + as shown in the following formula. 0.5 glucose + NADH + H + + + ATP ⁇ glycerin + NAD + + ADP + Pi
- acetyl coenzyme A is synthesized from acetic acid by acetyl-CoA synthase, and acetaldehyde is converted to ethanol, so that the following reaction formula is finally obtained, and excess coenzyme NADH is oxidized simultaneously with acetic acid. Is also metabolized.
- Non-Patent Document 5 and Patent Document 2 are not reports on xylose-utilizing yeast, and it is unclear whether they are effective at the time of xylose utilization.
- Non-patent Document 6 There is also a report of introducing the mhpF gene into non-destructive strains of the GPD1 gene and GPD2 gene (Non-patent Document 6). However, Non-Patent Document 6 does not report that the amount of acetic acid in the medium is reduced, although the amount of acetic acid produced is reduced by the introduction of the mhpF gene. Furthermore, this non-patent document 6 is also not a report on xylose-utilizing yeast.
- the present invention is particularly concerned with the production of ethanol using recombinant yeast capable of reducing acetic acid concentration by metabolizing acetic acid in the medium during xylose utilization and ethanol fermentation in yeast having xylose metabolism ability. It aims to provide a method.
- a recombinant yeast that introduces a specific acetaldehyde dehydrogenase gene into a yeast having the ability to metabolize xylose undergoes ethanol fermentation in a medium containing xylose.
- the inventors have found that acetic acid in the medium can be metabolized and have completed the present invention.
- the present invention includes the following.
- a method for producing ethanol comprising a step of culturing a recombinant yeast introduced with a xylose isomerase gene and an acetaldehyde dehydrogenase gene in a medium containing xylose and performing ethanol fermentation.
- xylose isomerase gene is a gene encoding the following protein (a) or (b).
- a protein having the amino acid sequence shown in SEQ ID NO: 4 (b) a protein having an amino acid sequence having 70% or more identity to the amino acid sequence shown in SEQ ID NO: 4 and having an enzyme activity for converting xylose into xylulose
- acetaldehyde dehydrogenase derived from E. coli is the following protein (a) or (b): (a) a protein having the amino acid sequence shown in SEQ ID NO: 2 or 20 (b) having an amino acid sequence having 70% or more identity to the amino acid sequence shown in SEQ ID NO: 2 or 20, and having acetaldehyde dehydrogenase activity Protein
- acetaldehyde dehydrogenase derived from Clostridium beijerinckii is the following protein (a) or (b): (a) a protein having the amino acid sequence shown in SEQ ID NO: 22 (b) a protein having an amino acid sequence having 70% or more identity to the amino acid sequence shown in SEQ ID NO: 22 and having acetaldehyde dehydrogenase activity
- acetaldehyde dehydrogenase derived from Chlamydomonas reinhardtii is the following protein (a) or (b): (a) a protein having the amino acid sequence shown in SEQ ID NO: 24 (b) a protein having an amino acid sequence having 70% or more identity to the amino acid sequence shown in SEQ ID NO: 24 and having acetaldehyde dehydrogenase activity
- the enzyme group constituting the non-oxidation process pathway in the pentose phosphate pathway is ribose-5-phosphate isomerase, ribulose-5-phosphate-3-epimerase, transketolase, and transaldolase.
- the concentration of acetic acid in the medium can be reduced, and fermentation inhibition caused by acetic acid can be effectively avoided.
- the method for producing ethanol according to the present invention can maintain high efficiency of ethanol fermentation using xylose as a sugar source, and can achieve an excellent ethanol yield. Therefore, the method for producing ethanol according to the present invention can reduce the amount of acetic acid brought in, for example, when reusing recombinant yeast or using it for continuous culture, and maintain an excellent ethanol yield. Can do.
- the method for producing ethanol according to the present invention is a method for synthesizing ethanol from a sugar source contained in a culture medium using a recombinant yeast having xylose metabolic ability and introduced with an acetaldehyde dehydrogenase gene.
- the ethanol production method according to the present invention is characterized in that acetic acid contained in a medium can be metabolized by the recombinant yeast, and the concentration of acetic acid in the medium decreases with ethanol fermentation.
- the recombinant yeast used in the ethanol production method according to the present invention is a yeast into which a xylose isomerase gene and an acetaldehyde dehydrogenase gene have been introduced, and has the ability to metabolize xylose.
- a yeast having xylose metabolism ability is a yeast to which xylose metabolism ability is imparted by introducing a xylose isomerase gene into a yeast that does not have xylose metabolism ability.
- Yeast having the ability to metabolize xylose can assimilate xylose contained in the medium to produce ethanol.
- the xylose contained in the medium may be obtained by a process of saccharifying xylan, hemicellulose or the like containing xylose as a constituent sugar, or xylan or hemicellulose or the like contained in the medium is saccharified by a saccharifying enzyme. May be supplied to the medium. In the latter case, it means a so-called simultaneous saccharification and fermentation system.
- the xylose isomerase gene (XI gene) is not particularly limited, and any biological species-derived gene may be used.
- a plurality of xylose isomerase genes derived from termite intestinal protists disclosed in JP 2011-147445 A can be used without particular limitation.
- the xylose isomerase gene is derived from the anaerobic mold Piromyces sp. E2 (Special Table 2005-514951), from the anaerobic mold Cyllamyces aberensis, and from bacteria.
- a gene derived from a Bacteroides thetaiotaomicron, a bacterium Clostridium phytofermentas, or a Streptomyces murinus cluster can also be used.
- xylose isomerase gene it is preferable to use a xylose isomerase gene derived from a wild termite (Reticulitermes speratus) intestinal protist.
- the base sequence of the coding region of the xylose isomerase gene derived from the intestinal protists of this Yamato termite (Reticulitermes speratus) and the amino acid sequence of the protein encoded by the gene are shown in SEQ ID NOs: 3 and 4, respectively.
- the xylose isomerase gene is not limited to those specified by SEQ ID NOs: 3 and 4, but may be a gene having a different base sequence or amino acid sequence but a paralogous relationship or a narrowly defined homologous relationship.
- the xylose isomerase gene is not limited to those specified in SEQ ID NOs: 3 and 4, for example, 70% or more, preferably 80% or more, more preferably 90%, with respect to the amino acid sequence of SEQ ID NO: 4. As described above, it may be one that encodes a protein having an amino acid sequence having 95% or more sequence similarity or identity and having xylose isomerase activity. Sequence similarity and identity values can be calculated by the BLASTN or BLASTX program that implements the BLAST algorithm (default setting). In addition, the value of sequence similarity was calculated by comparing the total of amino acid residues that completely matched when paired amino acid sequences were subjected to pair-wise alignment analysis and amino acid residues having similar physicochemical functions.
- the identity value is calculated as the ratio of the number of amino acid residues in all amino acid residues compared by calculating the amino acid residues that completely match when a pair of amino acid sequences are subjected to pair-wise alignment analysis. .
- the xylose isomerase gene is not limited to those specified in these SEQ ID NOs: 3 and 4, and for example, one or several amino acids are substituted, deleted, inserted, or inserted into the amino acid sequence of SEQ ID NO: 4. It may be a protein that has an added amino acid sequence and encodes a protein having acetaldehyde dehydrogenase activity.
- severe means, for example, 2 to 30, preferably 2 to 20, more preferably 2 to 10, and most preferably 2 to 5.
- the xylose isomerase gene is not limited to those specified in SEQ ID NOs: 3 and 4, and for example, stringent to all or part of the complementary strand of DNA consisting of the base sequence of SEQ ID NO: 3. It may be a protein that hybridizes under various conditions and encodes a protein having xylose isomerase activity.
- stringent conditions as used herein means the conditions under which a so-called specific hybrid is formed and a non-specific hybrid is not formed, and is appropriately determined with reference to, for example, Molecular Cloning: A Laboratory Manual (Third Edition) can do.
- the stringency can be set according to the temperature at the time of Southern hybridization and the salt concentration contained in the solution, and the temperature at the time of the washing step of Southern hybridization and the salt concentration contained in the solution. More specifically, as stringent conditions, for example, the sodium concentration is 25 to 500 mM, preferably 25 to 300 mM, and the temperature is 42 to 68 ° C., preferably 42 to 65 ° C. More specifically, it is 5 ⁇ SSC (83 mM NaCl, 83 mM sodium citrate), and the temperature is 42 ° C.
- a gene having a base sequence different from SEQ ID NO: 3 or a gene encoding an amino acid sequence different from SEQ ID NO: 4 functions as a xylose isomerase gene depends on whether the gene is an appropriate promoter and terminator.
- An expression vector incorporated between the cells may be prepared, and a host such as E. coli may be transformed using the expression vector, and the xylose isomerase activity of the expressed protein may be measured.
- the xylose isomerase activity means an activity for isomerizing xylose into xylulose.
- the xylose isomerase activity can be evaluated by preparing a solution containing xylose as a substrate, allowing the protein to be tested to act at an appropriate temperature, and measuring the amount of xylose decreased and / or the amount of xylulose produced.
- the xylose isomerase gene is a gene encoding a mutant xylose isomerase having an amino acid sequence in which a specific mutation is introduced into a specific amino acid residue in the amino acid sequence shown in SEQ ID NO: 4 and having improved xylose isomerase activity. It is preferable to use it.
- examples of the gene encoding mutant xylose isomerase include a gene encoding an amino acid sequence in which the 337th asparagine in the amino acid sequence shown in SEQ ID NO: 4 is substituted with cysteine.
- a xylose isomerase consisting of an amino acid sequence in which the 337th asparagine in the amino acid sequence shown in SEQ ID NO: 4 is substituted with cysteine has an excellent xylose isomerase activity as compared with a wild type xylose isomerase.
- the mutant xylose isomerase is not limited to those obtained by substituting the 337th asparagine with cysteine, but may be one obtained by substituting the 337th asparagine with an amino acid other than cysteine.
- a different amino acid residue may be substituted with another amino acid, or another amino acid residue other than the 337th asparagine may be substituted.
- genes related to xylose metabolism other than xylose isomerase gene include xylose reductase gene encoding xylose reductase that converts xylose to xylitol, xylitol dehydrogenase gene encoding xylitol dehydrogenase that converts xylitol to xylulose, and xylulose. It is meant to include a xylulokinase gene encoding xylulokinase that produces xylulose 5-phosphate. Xylulose 5-phosphate produced by xylulokinase enters the pentose phosphate pathway and is metabolized.
- genes related to xylose metabolism include, but are not limited to, xylose reductase gene and xylitol dehydrogenase gene derived from Pichia stipitis, and xylulokinase gene derived from Saccharomyces cerevisiae (Eliasson A. et al., Appl. Environ. Microbiol 66: 3381-3386 and Toivari MN et al., Metab. Eng. 3: 236-249).
- a xylose reductase gene derived from Candida ⁇ ⁇ ⁇ tropicalis or Candida prapsilosis can be used as the xylose reductase gene.
- xylitol dehydrogenase gene a xylitol dehydrogenase gene derived from Candida tropicalis or Candida prapsilosis can be used.
- xylulokinase gene a xylulokinase gene derived from Pichia stipitis can also be used.
- yeasts that inherently have the ability to metabolize xylose include, but are not limited to, Pichia stipitis, Candida tropicalis, Candida prapsilosis, and the like.
- the acetaldehyde dehydrogenase gene to be introduced into yeast having xylose metabolic ability is not particularly limited, and any organism-derived gene may be used.
- the acetaldehyde dehydrogenase gene is modified in accordance with the codon usage in the yeast to be introduced when using genes derived from organisms other than fungi such as yeast, such as bacteria, animals, plants, insects, and algae. It is preferable to use the gene obtained.
- the acetaldehyde dehydrogenase gene includes the mhpF gene in E. coli and ALDH1 in Entamoeba histolytica as disclosed in Applied and Environmental Microbiology, May 2004, p. 2892-2897, Vol. 70, No. 5. Genes can be used.
- the base sequence of the mhpF gene in Escherichia coli and the amino acid sequence of the protein encoded by the mhpF gene are shown in SEQ ID NOs: 1 and 2, respectively.
- the acetaldehyde dehydrogenase gene is not limited to those specified in SEQ ID NOS: 1 and 2, and the nucleotide sequence and amino acid sequence are not limited as long as the enzyme is defined in EC number 1.2.1.10. It may be a gene that is different but has a paralogous relationship or a homologous relationship in a narrow sense.
- Examples of the acetaldehyde dehydrogenase gene include an adhE gene in Escherichia coli, an acetaldehyde dehydrogenase gene derived from Clostridium beijerinckii, and an acetaldehyde dehydrogen gene derived from Chlamydomonas reinhardtii.
- nucleotide sequence of the adhE gene in E. coli and the amino acid sequence of the protein encoded by the adhE gene are shown in SEQ ID NOs: 19 and 20, respectively.
- nucleotide sequence of the acetaldehyde dehydrogen gene derived from Clostridium beijerinckii and the amino acid sequence of the protein encoded by this gene are shown in SEQ ID NOs: 21 and 22, respectively.
- base sequence of the acetaldehyde dehydrogen gene derived from Chlamydomonas reinhardtii and the amino acid sequence of the protein encoded by this gene are shown in SEQ ID NOs: 23 and 24, respectively.
- the acetaldehyde dehydrogenase gene is not limited to those specified in SEQ ID NOs: 1 and 2, 19 and 20, 21 and 22, and 23 and 24. It has an amino acid sequence having a sequence similarity or identity of 70% or more, preferably 80% or more, more preferably 90% or more, and most preferably 95% or more with respect to the amino acid sequence, and has acetaldehyde dehydrogenase activity. It may be one that encodes a protein. Sequence similarity and identity values can be calculated by the BLASTN or BLASTX program that implements the BLAST algorithm (default setting).
- sequence similarity was calculated by comparing the total of amino acid residues that completely matched when paired amino acid sequences were subjected to pair-wise alignment analysis and amino acid residues having similar physicochemical functions. Calculated as a percentage of the total number of all amino acid residues.
- identity value is calculated as the ratio of the number of amino acid residues in all amino acid residues compared by calculating the amino acid residues that completely match when a pair of amino acid sequences are subjected to pair-wise alignment analysis. .
- acetaldehyde dehydrogenase gene is not limited to those specified in SEQ ID NOs: 1 and 2, 19 and 20, 21 and 22, and 23 and 24.
- the amino acid sequence may have an amino acid sequence in which one or several amino acids are substituted, deleted, inserted or added, and may encode a protein having acetaldehyde dehydrogenase activity.
- severe means, for example, 2 to 30, preferably 2 to 20, more preferably 2 to 10, and most preferably 2 to 5.
- the acetaldehyde dehydrogenase gene is not limited to those specified in these SEQ ID NOs: 1 and 2, 19 and 20, 21 and 22, and 23 and 24.
- SEQ ID NOs: 1, 19, 21 or 23 It may be one that hybridizes under stringent conditions to all or part of the complementary strand of DNA consisting of the nucleotide sequence of and encodes a protein having acetaldehyde dehydrogenase activity.
- stringent conditions as used herein means the conditions under which a so-called specific hybrid is formed and a non-specific hybrid is not formed, and is appropriately determined with reference to, for example, Molecular Cloning: A Laboratory Manual (Third Edition) can do.
- the stringency can be set according to the temperature at the time of Southern hybridization and the salt concentration contained in the solution, and the temperature at the time of the washing step of Southern hybridization and the salt concentration contained in the solution. More specifically, as stringent conditions, for example, the sodium concentration is 25 to 500 mM, preferably 25 to 300 mM, and the temperature is 42 to 68 ° C., preferably 42 to 65 ° C. More specifically, it is 5 ⁇ SSC (83 mM NaCl, 83 mM sodium citrate), and the temperature is 42 ° C.
- a gene having a nucleotide sequence different from SEQ ID NO: 1, 19, 21 or 23, or a gene encoding an amino acid sequence different from SEQ ID NO: 2, 20, 22 or 24 functions as an acetaldehyde dehydrogenase gene.
- an expression vector in which the gene is inserted between an appropriate promoter and terminator, etc. and transform the host such as E. coli using this expression vector, and acetaldehyde dehydrogenase of the expressed protein What is necessary is just to measure activity.
- acetaldehyde dehydrogenase activity a solution containing acetaldehyde, CoA and NAD + as a substrate is prepared, the protein to be tested is allowed to act at an appropriate temperature, and the produced acetyl phosphate is converted into acetylphosphoric acid by the action of phosphoacetyltransferase. It can be measured by converting it to an acid, or the produced NADH can be measured spectroscopically.
- the recombinant yeast used in the method for producing ethanol according to the present invention is a yeast having xylose metabolism ability, introduced with at least an acetaldehyde dehydrogenase gene, and further introduced with other genes. There may be. Although it does not specifically limit as another gene, For example, you may introduce
- the recombinant yeast can be a yeast having ⁇ -glucosidase activity by introducing a ⁇ -glucosidase gene.
- ⁇ -glucosidase activity means an activity catalyzing a reaction of hydrolyzing a ⁇ -glycoside bond of a sugar. That is, ⁇ -glucosidase can decompose cellooligosaccharides such as cellobiose into glucose.
- the ⁇ -glucosidase gene can also be introduced as a cell surface display type gene.
- the cell surface display type gene is a gene modified so that a protein encoded by the gene is expressed so as to be displayed on the surface layer of the cell.
- the cell surface-presenting ⁇ -glucosidase gene is a gene obtained by fusing a ⁇ -glucosidase gene and a cell surface localized protein gene.
- the cell surface localized protein refers to a protein that is fixed on the cell surface layer of yeast and is present on the cell surface layer.
- ⁇ - or a-agglutinin which is an aggregating protein, FLO protein and the like can be mentioned.
- a cell surface localized protein has a secretory signal sequence on the N-terminal side and a GPI anchor attachment recognition signal on the C-terminal side. Although it has the same secretory protein in that it has a secretion signal, the cell surface localized protein is different from the secreted protein in that it is transported by being immobilized on the cell membrane via a GPI anchor.
- the GPI anchor attachment recognition signal sequence is selectively cleaved, and is bound to the GPI anchor at the newly protruding C-terminal portion and fixed to the cell membrane. Thereafter, the base of the GPI anchor is cleaved by phosphatidylinositol-dependent phospholipase C (PI-PLC). Next, the protein cut off from the cell membrane is incorporated into the cell wall, fixed to the cell surface layer, and localized on the cell surface layer (see, for example, JP-A-2006-174767).
- PI-PLC phosphatidylinositol-dependent phospholipase C
- the ⁇ -glucosidase gene is not particularly limited, and examples thereof include ⁇ -glucosidase genes derived from Aspergillus aculeatus (Murai et al., Appl. Environ. Microbiol. 64: 4857-4861).
- ⁇ -glucosidase gene a ⁇ -glucosidase gene derived from Aspergillus oryzae, a ⁇ -glucosidase gene derived from Clostridium cellulovorans, a ⁇ -glucosidase gene derived from Saccharomycopsis fibligera, and the like can be used.
- the recombinant yeast used in the method for producing ethanol according to the present invention may be one in which a gene encoding another enzyme constituting cellulase is introduced in addition to or in addition to the ⁇ -glucosidase gene.
- cellulase is composed of exo-type cellobiohydrolase (CBH1 and CBH2) that releases cellobiose from the end of crystalline cellulose, and amorphous cellulose (amorphous cellulose) chains are randomized, although crystalline cellulose cannot be degraded.
- CBH1 and CBH2 exo-type cellobiohydrolase
- amorphous cellulose (amorphous cellulose) chains are randomized, although crystalline cellulose cannot be degraded.
- An endo-type endoglucanase (EG) that cleaves can be mentioned.
- genes to be introduced into the recombinant yeast include an alcohol dehydrogenase gene (ADH1 gene) that has the activity of converting acetaldehyde into ethanol, and an acetyl-CoA synthase gene that has the activity of converting acetic acid into acetyl-CoA. (ACS1 gene) and genes (ALD4 gene, ALD5 gene and ALD6 gene) having an activity of converting acetaldehyde into acetic acid.
- ADH2 gene which has the activity which converts ethanol into acetaldehyde.
- the recombinant yeast used in the method for producing ethanol according to the present invention preferably has a characteristic of highly expressing an alcohol dehydrogenase gene (ADH1 gene) having an activity of converting acetaldehyde into ethanol.
- ADH1 gene alcohol dehydrogenase gene
- Examples of high expression of the gene include a method in which the promoter of the gene of interest is replaced with a promoter for high expression, or an expression vector that can express the gene is introduced into yeast.
- the nucleotide sequence of the ADH1 gene of Saccharomyces cerevisiae and the amino acid sequence of the protein encoded by the gene are shown in SEQ ID NOs: 5 and 6, respectively.
- the alcohol dehydrogenase gene to be highly expressed is not limited to those specified by SEQ ID NOs: 5 and 6, but has different base sequences and amino acid sequences but has a paralogous relationship or a narrowly defined homologous relationship. It may be.
- the alcohol dehydrogenase gene is not limited to those specified in SEQ ID NOs: 5 and 6, for example, 70% or more, preferably 80% or more, more preferably, relative to the amino acid sequence of SEQ ID NO: 6. It may encode a protein having an amino acid sequence having a sequence similarity or identity of 90% or more, most preferably 95% or more, and having alcohol dehydrogenase activity. Sequence similarity and identity values can be calculated by the BLASTN or BLASTX program that implements the BLAST algorithm (default setting). In addition, the value of sequence similarity was calculated by comparing the total of amino acid residues that completely matched when paired amino acid sequences were subjected to pair-wise alignment analysis and amino acid residues having similar physicochemical functions.
- the identity value is calculated as the ratio of the number of amino acid residues in all amino acid residues compared by calculating the amino acid residues that completely match when a pair of amino acid sequences are subjected to pair-wise alignment analysis. .
- the alcohol dehydrogenase gene is not limited to those specified in SEQ ID NOs: 5 and 6, for example, one or several amino acids are substituted, deleted, or deleted from the amino acid sequence of SEQ ID NO: 6. It may have an amino acid sequence inserted or added and encodes a protein having alcohol dehydrogenase.
- severe means, for example, 2 to 30, preferably 2 to 20, more preferably 2 to 10, and most preferably 2 to 5.
- the alcohol dehydrogenase gene is not limited to those specified in SEQ ID NOs: 5 and 6, for example, with respect to all or part of the complementary strand of DNA consisting of the base sequence of SEQ ID NO: 5, It may be one that hybridizes under stringent conditions and encodes a protein having alcohol dehydrogenase activity.
- stringent conditions as used herein means the conditions under which a so-called specific hybrid is formed and a non-specific hybrid is not formed, and is appropriately determined with reference to, for example, Molecular Cloning: A Laboratory Manual (Third Edition) can do.
- the stringency can be set according to the temperature at the time of Southern hybridization and the salt concentration contained in the solution, and the temperature at the time of the washing step of Southern hybridization and the salt concentration contained in the solution. More specifically, as stringent conditions, for example, the sodium concentration is 25 to 500 mM, preferably 25 to 300 mM, and the temperature is 42 to 68 ° C., preferably 42 to 65 ° C. More specifically, it is 5 ⁇ SSC (83 mM NaCl, 83 mM sodium citrate), and the temperature is 42 ° C.
- a gene having a base sequence different from SEQ ID NO: 5 or a gene encoding an amino acid sequence different from SEQ ID NO: 6 functions as an alcohol dehydrogenase gene having an activity of converting acetaldehyde into ethanol.
- an expression vector in which the gene is inserted between an appropriate promoter and terminator, etc., and a host such as yeast is transformed using this expression vector, and the alcohol dehydrogenase activity of the expressed protein is measured. do it.
- Alcohol dehydrogenase activity to convert acetaldehyde to ethanol is prepared by preparing a solution containing aldehyde and NADH or NADPH as a substrate, allowing the protein to be tested to act at an appropriate temperature, measuring the alcohol produced, or NAD + or NADP + can be measured spectroscopically.
- the recombinant yeast used in the method for producing ethanol according to the present invention preferably has a characteristic that the expression level of an alcohol dehydrogenase gene (ADH2 gene) having an activity of converting ethanol into an aldehyde is reduced.
- ADH2 gene an alcohol dehydrogenase gene having an activity of converting ethanol into an aldehyde
- methods such as altering the promoter of the gene of interest and deleting the gene can be mentioned.
- the gene is deleted, one of the pair of ADH2 genes present in the diploid recombinant yeast may be deleted, or both may be deleted.
- Methods for suppressing gene expression include the so-called transposon method, transgene method, post-transcriptional gene silencing method, RNAi method, nonsense-mediated decay (NNM) method, ribozyme method, antisense method, miRNA ( micro-RNA) method, siRNA (small interfering RNA) method and the like.
- the base sequence of the ADH2 gene of Saccharomyces cerevisiae and the amino acid sequence of the protein encoded by the gene are shown in SEQ ID NOs: 7 and 8, respectively.
- the target alcohol dehydrogenase gene is not limited to those specified in SEQ ID NOs: 7 and 8, but is a gene that has a different base sequence or amino acid sequence but has a paralogous relationship or a narrowly-defined homologous relationship. May be.
- the alcohol dehydrogenase gene is not limited to those specified in SEQ ID NOs: 7 and 8, for example, 70% or more, preferably 80% or more, more preferably, relative to the amino acid sequence of SEQ ID NO: 8. It may encode a protein having an amino acid sequence having a sequence similarity or identity of 90% or more, most preferably 95% or more, and having alcohol dehydrogenase activity. Sequence similarity and identity values can be calculated by the BLASTN or BLASTX program that implements the BLAST algorithm (default setting). In addition, the value of sequence similarity was calculated by comparing the total of amino acid residues that completely matched when paired amino acid sequences were subjected to pair-wise alignment analysis and amino acid residues having similar physicochemical functions.
- the identity value is calculated as the ratio of the number of amino acid residues in all amino acid residues compared by calculating the amino acid residues that completely match when a pair of amino acid sequences are subjected to pair-wise alignment analysis. .
- the alcohol dehydrogenase gene is not limited to those specified in SEQ ID NOs: 7 and 8, and for example, one or several amino acids are substituted, deleted, or deleted from the amino acid sequence of SEQ ID NO: 8. It may have an amino acid sequence inserted or added and encodes a protein having alcohol dehydrogenase activity.
- severe means, for example, 2 to 30, preferably 2 to 20, more preferably 2 to 10, and most preferably 2 to 5.
- the alcohol dehydrogenase gene is not limited to those specified in SEQ ID NOs: 7 and 8, for example, with respect to all or part of the complementary strand of DNA consisting of the base sequence of SEQ ID NO: 7. It may be one that hybridizes under stringent conditions and encodes a protein having alcohol dehydrogenase activity.
- stringent conditions as used herein means the conditions under which a so-called specific hybrid is formed and a non-specific hybrid is not formed, and is appropriately determined with reference to, for example, Molecular Cloning: A Laboratory Manual (Third Edition) can do.
- the stringency can be set according to the temperature at the time of Southern hybridization and the salt concentration contained in the solution, and the temperature at the time of the washing step of Southern hybridization and the salt concentration contained in the solution. More specifically, as stringent conditions, for example, the sodium concentration is 25 to 500 mM, preferably 25 to 300 mM, and the temperature is 42 to 68 ° C., preferably 42 to 65 ° C. More specifically, it is 5 ⁇ SSC (83 mM NaCl, 83 mM sodium citrate), and the temperature is 42 ° C.
- a gene having a base sequence different from SEQ ID NO: 7 or a gene encoding an amino acid sequence different from SEQ ID NO: 8 functions as an alcohol dehydrogenase gene having an activity of converting ethanol to aldehyde Or an expression vector in which the gene is inserted between an appropriate promoter and terminator, etc., and a host such as yeast is transformed using this expression vector, and the alcohol dehydrogenase activity of the expressed protein is measured. do it.
- Alcohol dehydrogenase activity to convert ethanol into aldehyde is prepared by preparing a solution containing alcohol and NAD + or NADP + as a substrate, allowing the protein to be tested to act at an appropriate temperature, measuring the aldehyde produced, or NADH or NADPH Can be measured spectroscopically.
- genes introduced into the recombinant yeast include genes involved in the metabolic pathway of L-arabinose, which is a pentose contained in hemicellulose constituting biomass.
- L-arabinose is a pentose contained in hemicellulose constituting biomass.
- examples of such genes include prokaryotic L-arabinose isomerase gene, L-librokinase gene, L-ribulose-5-phosphate 4-epimerase gene, and eukaryotic L-arabitol-4-dehydrogenase.
- Gene and L-xylose reductase gene include prokaryotic L-arabinose isomerase gene, L-librokinase gene, L-ribulose-5-phosphate 4-epimerase gene, and eukaryotic L-arabitol-4-dehydrogenase.
- genes to be introduced into the recombinant yeast include genes that can promote the use of xylose in the medium.
- genes that can promote the use of xylose in the medium.
- Specific examples include a gene encoding xylulokinase having an activity of producing xylulose-5-phosphate using xylulose as a substrate.
- a gene encoding an enzyme selected from the group of enzymes constituting the non-oxidation process pathway in the pentose phosphate pathway can be introduced.
- the enzyme constituting the non-oxidation process pathway in the pentose phosphate pathway include ribose-5-phosphate isomerase, ribulose-5-phosphate-3-epimerase, transketolase, and transaldolase. It is preferable to introduce one or more genes encoding these enzymes. Moreover, it is more preferable to introduce two or more of these genes in combination, more preferable to introduce three or more in combination, and most preferable to introduce all types of genes.
- the xylulokinase (XK) gene can be used without any limitation on the organism of origin.
- the XK gene is held by many microorganisms such as bacteria and yeast that assimilate xylulose. Information on the XK gene can be obtained as appropriate by searching for NCBI HP or the like.
- XK genes derived from yeast, lactic acid bacteria, Escherichia coli, plants and the like can be mentioned.
- Examples of the XK gene include XKS1 (GenBank: Z72979) (base sequence and amino acid sequence of CDS coding region), which is an XK gene derived from S. cerevisiae S288C strain.
- transaldolase (TAL) gene transketolase (TKL) gene
- ribulose-5-phosphate epimerase (RPE) gene ribose-5-phosphate ketoisomerase (RKI) gene
- TAL transaldolase
- TKL transketolase
- RPE ribulose-5-phosphate epimerase
- RKI ribose-5-phosphate ketoisomerase
- genes derived from the same genus as the host eukaryotic cell such as eukaryotic cells or yeast, more preferably from the same species as the host eukaryotic cell.
- the TAL1 gene can be preferably used as the TAL gene, the TKL1 and TKL2 genes as the TKL gene, the RPE1 gene as the RPE gene, and the RKI1 gene as the RKI gene.
- these genes include the TAL1 gene (GenBank: U19102) which is a TAL1 gene derived from the S. cerevisiae S288 strain, the TKL1 gene (GenBank: X73224) derived from the S. cerevisiae S288 strain, and the RPE1 gene derived from the S. cerevisiae S288 strain. (Genbank: X83571), RKI1 gene (GenBank: Z75003) derived from S. cerevisiae S288 strain.
- a recombinant yeast that can be used in the present invention can be produced.
- the xylose isomerase gene and the acetaldehyde dehydrogenase gene may be introduced into yeast that does not have xylose metabolism ability, may be introduced into yeast that originally has xylose metabolism ability, or have xylose metabolism ability. You may introduce
- all the genes may be introduced simultaneously or sequentially using different expression vectors.
- yeasts such as Candida Shehatae, Pichia stipitis, Pachysolen tannophilus, Saccharomyces cerevisiae and Schizosaccaromyces pombe, and Saccharomyces cerevisiae is particularly preferable.
- the yeast may be an experimental strain used for experimental convenience, or an industrial strain (practical strain) used for practical utility. Examples of industrial strains include yeast strains used for wine, sake and shochu making.
- yeast having homothallic properties is synonymous with homothallic yeast.
- the yeast having homothallic properties is not particularly limited, and any yeast can be used. Examples of yeast having homothallic properties include, but are not limited to, Saccharomyces cerevisiae ⁇ OC-2 strain (NBRC2260).
- yeasts with homothallic properties include alcoholic yeasts (Taken 396, NBRC0216) (Source: “Characteristics of Alcoholic Yeast”, Sakekenkai Bulletin, No37, p18-22 (1998.8)), isolated in Brazil and Okinawa Ethanol producing yeast (Source: “Genetic properties of wild strains of Saccharomyces cerevisiae isolated in Brazil and Okinawa” Journal of Japanese Agricultural Chemical Society, Vol.65, No.4, p759-762 (1991.4)) and 180 (Source: Alcohol The screening of yeast having a strong fermenting ability ”, Journal of Japan Brewing Association, Vol.82, No.6, p439-443 (1987.6)).
- yeast having homothallic properties can be used as a yeast having homothallic properties by introducing the HO gene so that it can be expressed. That is, in the present invention, the yeast having homothallic properties is meant to include yeast into which the HO gene has been introduced so as to be expressed.
- the Saccharomyces cerevisiae OC-2 strain is preferable because it is a strain that has been confirmed to be safe and has been used in the winemaking scene. Further, the Saccharomyces cerevisiae OC-2 strain is preferable because it has excellent promoter activity under high sugar concentration conditions, as shown in the Examples described later. In particular, the Saccharomyces cerevisiae OC-2 strain is preferable because it has an excellent promoter activity of the pyruvate decarboxylase gene (PDC1) under high sugar concentration conditions.
- PDC1 pyruvate decarboxylase gene
- the promoter of the gene to be introduced is not particularly limited.
- the promoter of glyceraldehyde 3-phosphate dehydrogenase gene (TDH3), the promoter of 3-phosphoglycerate kinase gene (PGK1), the hyperosmotic response 7 gene ( HOR7) promoters can be used.
- the pyruvate decarboxylase gene (PDC1) promoter is preferred because of its high ability to highly express a downstream target gene.
- the above-described gene may be introduced into the yeast genome together with a promoter controlling expression and other expression control regions.
- the above-described gene may be introduced so that the expression is controlled by a promoter of a gene originally present in the genome of yeast as a host or other expression control regions.
- any conventionally known method known as a yeast transformation method can be applied. Specifically, for example, electroporation method “Meth. Enzym., 194, p182 (1990)”, spheroplast method “Proc. Natl. Acad. Sci. USA, 75 p1929 (1978)”, acetic acid Lithium Method “J. Bacteriology, 153, p163 (1983)”, Proc. Natl. Acad. Sci. USA, 75 p1929 (1978), Methods in yeast genetics, 2000 Edition: A Cold Spring Harbor Laboratory Course Manual The method can be implemented, but is not limited thereto.
- ethanol fermentation culture is performed in a medium containing at least xylose. That is, the medium for ethanol fermentation contains at least xylose as a carbon source. Note that the medium may contain other carbon sources such as glucose in advance.
- xylose contained in the medium used for ethanol fermentation can be derived from biomass.
- the medium used for ethanol fermentation may have a composition including cellulosic biomass and hemicellulase that saccharifies hemicellulose contained in the cellulosic biomass to produce xylose.
- the cellulosic biomass a conventionally known pretreatment may be applied. Although it does not specifically limit as pre-processing, For example, the process which decomposes
- a treatment such as a treatment in which the pulverized cellulose biomass is immersed in a dilute sulfuric acid solution, an alkali solution or an ionic liquid, a hydrothermal treatment, or a fine pulverization treatment may be applied.
- a treatment such as a treatment in which the pulverized cellulose biomass is immersed in a dilute sulfuric acid solution, an alkali solution or an ionic liquid, a hydrothermal treatment, or a fine pulverization treatment may be applied.
- the composition which contains a cellulose and a cellulase further may be sufficient as the said culture medium.
- the medium contains glucose produced by cellulase acting on cellulose.
- the culture medium used for ethanol fermentation contains cellulose
- the cellulose can be derived from biomass.
- the medium used for ethanol fermentation may have a composition containing cellulase capable of saccharifying cellulase contained in cellulosic biomass.
- a saccharified solution after saccharification treatment of cellulosic biomass may be added to the medium used for ethanol fermentation.
- the saccharified solution contains residual cellulose or cellulase and xylose derived from hemicellulose contained in the cellulosic biomass.
- the method for producing ethanol according to the present invention includes at least a step of ethanol fermentation using xylose as a sugar source.
- the ethanol production method according to the present invention can produce ethanol by ethanol fermentation using xylose as a sugar source.
- ethanol is recovered from the medium after ethanol fermentation.
- the method for recovering ethanol is not particularly limited, and any conventionally known method can be applied.
- a liquid layer containing ethanol and a solid layer containing recombinant yeast and solid components are separated by solid-liquid separation operation. Thereafter, ethanol contained in the liquid layer is separated and purified by a distillation method, whereby high purity ethanol can be recovered.
- the purity of ethanol can be adjusted as appropriate according to the intended use of ethanol.
- fermentation inhibitors such as acetic acid and furfural may be produced in the pretreatment and saccharification treatment described above.
- acetic acid is known to inhibit the growth and proliferation of yeast and to reduce the efficiency of ethanol fermentation using xylose as a sugar source.
- the ethanol production method according to the present invention can achieve an excellent ethanol yield as compared with the case of using yeast into which the xylose isomerase gene and the acetaldehyde dehydrogenase gene are not introduced.
- the method for producing ethanol since the concentration of acetic acid in the medium is low even after the recombinant yeast is cultured for a predetermined period, a new culture is performed using a part of the medium after the predetermined period of culture.
- the amount of acetic acid brought in can be reduced even if it is used in a continuous culture system that starts the process.
- the amount of acetic acid brought in can be reduced for the same reason even when the cells are collected and reused after the ethanol fermentation process is completed.
- the method for producing ethanol according to the present invention is a so-called saccharification of cellulose contained in a medium with cellulase and a so-called ethanol fermentation process using xylose and glucose produced by saccharification as a sugar source. It may be a simultaneous saccharification and fermentation treatment.
- the simultaneous saccharification and fermentation treatment means a treatment that is carried out simultaneously without distinguishing between the step of saccharifying cellulosic biomass and the ethanol fermentation step.
- the saccharification method is not particularly limited, and examples thereof include an enzyme method using a cellulase preparation such as cellulase or hemicellulase.
- the cellulase preparation contains a plurality of enzymes involved in the degradation of cellulose chains and hemicellulose chains, and exhibits a plurality of activities such as endoglucanase activity, endoxylanase activity, cellobiohydrolase activity, glucosidase activity, and xylosidase activity.
- the cellulase preparation is not particularly limited, and examples thereof include cellulase produced by Trichoderma reesei, Acremonium cerulolyticus, and the like. As the cellulase preparation, a commercially available product may be used.
- a cellulase preparation and the above-described recombinant microorganism are added to a medium containing cellulosic biomass (which may be after pretreatment), and the recombinant yeast is cultured in a predetermined temperature range.
- the culture temperature is not particularly limited, but can be 25 to 45 ° C., preferably 30 to 40 ° C. in consideration of the efficiency of ethanol fermentation.
- the pH of the culture solution is preferably 4-6. Moreover, you may stir and shake in the case of culture
- an irregular simultaneous saccharification and fermentation may be used in which saccharification is first performed at the optimum temperature (40 to 70 ° C.) of the enzyme, and then the temperature is lowered to a predetermined temperature (30 to 40 ° C.) and yeast is added.
- Example 1 a recombinant yeast into which a xylose isomerase gene and an acetaldehyde dehydrogenase gene from Escherichia coli (mhpF gene) were introduced was prepared, and the ability of the recombinant yeast to metabolize acetate was evaluated.
- XKS1 gene introduction vector pUC-HIS3U-P_HOR7-XKS1-T_TDH3-P_TDH2-hph-T_CYC1-HIS3D shown in Fig. 1 was prepared as a yeast introduction vector for the xylulokinase (XK) gene derived from S. cerevisiae. did.
- This vector includes the XKS1 gene (genebank: X61377), an XK gene derived from the S.
- HOR7 promoter is added on the 5 ′ side and a TDH3 terminator is added on the 3 ′ side, and a homologous recombination region on the yeast genome.
- the myophosphotransferase (hph) gene (marker gene) is included.
- a site for the restriction enzyme Sse8387I was introduced outside the homologous recombination region.
- the nucleotide sequence of the coding region of the XKS1 gene derived from S. cerevisiae NBRC304 strain and the amino acid sequence of xylulokinase encoded by the gene are shown in SEQ ID NOs: 9 and 10, respectively.
- XI gene transfer vector As a vector for yeast introduction of xylose isomerase (RsXI-C1, see JP-A-2011-147445) gene derived from intestinal protists of Reticulitermes speratus, pUC-R67-HOR7p-RsXI-T_TDH3-TRP1d- shown in FIG. R45 was produced.
- the RsXI-C1 gene having a HOR7 promoter added on the 5 ′ side and a TDH3 terminator added on the 3 ′ side, and an rRNA gene (rDNA) that is a homologous recombination region on the yeast genome are R45.
- R67 and the TRP1d marker gene in which the promoter portion is deleted to reduce the expression level.
- a site for the restriction enzyme Sse8387I was introduced outside the homologous recombination region.
- R45 and R67 introduce multiple copies of the gene containing RsXI-C1 into the rDNA locus on chromosome 12.
- the TRP1d marker functions as a marker only when it is introduced into the chromosome in multiple copies. Therefore, multiple copies can be introduced by using this vector.
- the RsXI-C1 gene was designed by designing a base sequence in which the codons used for the entire region were matched to the yeast codon usage frequency, and were totally synthesized based on the base sequence.
- the nucleotide sequence of the RsXI-C1 gene designed in this example and the amino acid sequence of xylose isomerase encoded by the gene are shown in SEQ ID NOs: 3 and 4, respectively.
- TAL1 / TKL1 gene transfer vector As a vector for introducing yeast of transaldolase 1 (TAL1) gene and transketolase 1 (TKL1) gene derived from S. cerevisiae, pUC-LEU2U-P_HOR7-TAL1-T_TDH3-P_HOR7-TKL1-T_TDH3-HIS3- LEU2D was produced.
- This vector includes a TAL1 gene (genebank: U19102) derived from the S. cerevisiae S288 strain to which a HOR7 promoter is added on the 5 ′ side and a TDH3 terminator is added on the 3 ′ side; a HOR7 promoter and 3 ′ on the 5 ′ side.
- TKL1 gene (genebank: X73224), a TKL1 gene derived from S. cerevisiae S288 strain with TDH3 terminator added on the side; from the 3 ′ end of leucine synthase (LEU2) gene that is a homologous recombination region on the yeast genome A region of about 500 bp upstream (LEU2U) and a region of about 450 bp upstream of its gene 5 ′ end (LEU2D); and a histidine synthase (HIS3) gene (marker gene) are included. A site for the restriction enzyme Sse8387I was introduced outside the homologous recombination region.
- nucleotide sequence of the coding region of the TAL1 gene derived from S. cerevisiae S288 strain and the amino acid sequence of transaldolase 1 encoded by the gene are shown in SEQ ID NOs: 11 and 12, respectively. Furthermore, the nucleotide sequence of the coding region of the TKL1 gene derived from S. cerevisiae S288 strain and the amino acid sequence of transketolase 1 encoded by the gene are shown in SEQ ID NOs: 13 and 14, respectively.
- RPE1 / RKI1 gene introduction and GRE3 gene disruption As a vector for yeast introduction of ribulose phosphate epimerase 1 (RPE1) gene and ribose phosphate ketoisomerase (RKI1) gene derived from S. cerevisiae, the pUC- shown in FIG. GRE3U-P_HOR7-RPE1-T_TDH3-P_HOR7-RKI1-T_TDH3-LEU2-GRE3D was prepared.
- This vector includes an RPE1 gene (genebank: X83571), which is an RPE1 gene derived from the S.
- GRE3 gene which is a region for homologous recombination on the yeast genome and disruption of the aldose reductase 3 (GRE3) gene
- GRE3U aldose reductase 3
- LEU2 leucine synthase
- SEQ ID NOs: 15 and 16 respectively.
- nucleotide sequence of the coding region of RKI1 gene derived from S. cerevisiae S288 strain and the amino acid sequence of ribose phosphate ketoisomerase encoded by the gene are shown in SEQ ID NOs: 17 and 18, respectively.
- ADH2 gene disruption vector pCR-ADH2U-URA3-ADH2D shown in Fig. 5 was prepared as a vector for disrupting the ADH2 gene endogenous to the host.
- This vector includes a region of about 700 bp upstream of the ADH2 gene (ADH2U) and a region of about 800 bp downstream of the ADH2 gene as regions for homologous recombination into the yeast genome and disrupting the alcohol dehydrogenase 2 (ADH2) gene ( ADH2D), and orotidine-5′-phosphate decarboxylase (URA3) gene (marker gene).
- ADH1 gene introduction As a vector for yeast introduction of the alcohol dehydrogenase 1 (ADH1) gene, pCR-ADH2part-T_CYC1-P_TDH3-ADH1-T_ADH1-URA3-ADH2D shown in FIG. 6 was prepared.
- the ADH1 gene (genebank: Z74828.1) derived from the S. cerevisiae S288 strain added with the TDH3 promoter on the 5 ′ side and the ADH1 terminator on the 3 ′ side is a homologous recombination region on the yeast genome.
- a region about 450 bp upstream from the 3 ′ end of the ADH2 gene (ADH2part), a region about 700 bp downstream from the 3 ′ end (ADH2D), a CYC1 terminator as a terminator for ADH2, and the URA3 gene (marker gene) Yes.
- mhpF gene introduction vector pCR-ADH2part-T_CYC1-ERO1_T-mhpF-HOR7_P-URA3-ADH2D shown in FIG. 7 was prepared as a vector for yeast introduction of the acetaldehyde dehydrogenase (mhpF) gene derived from E. coli. .
- This vector contains the E. coli-derived acetaldehyde dehydrogenation gene (mhpF gene) with the HOR7 promoter added on the 5 'side and the ERO1 terminator on the 3' side, and the ADH2 gene that serves as a homologous recombination region on the yeast genome.
- the mhpF gene was designed by designing a base sequence in which the codons used were converted in accordance with the codon usage frequency of the yeast in the entire region, and using the total synthesis based on the base sequences.
- the nucleotide sequence of the mhpF gene designed in this example and the amino acid sequence of acetaldehyde dehydrogenase encoded by the gene are shown in SEQ ID NOs: 1 and 2, respectively.
- mhpF / ADH1 gene introduction vector As a yeast introduction vector for the mhpF and ADH1 genes, pCR-ADH2part-T_CYC1-P_TDH3-ADH1-T_ADH1-ERO1_T-mhpF-HOR7_P-URA3-ADH2D shown in FIG. 8 was prepared. .
- This vector has the mhpF gene with the HOR7 promoter added at the 5 ′ side and the ERO1 terminator added at the 3 ′ side (same as (7) above), the TDH3 promoter added at the 5 ′ side, and the ADH1 terminator added at the 3 ′ side.
- ADH288 strain (same as (6) above), a region about 450 bp upstream from the 3 ′ end of the ADH2 gene that serves as a homologous recombination region on the yeast genome (ADH2part), and 3 ′ side A region of about 700 bp downstream from the end (ADH2D), CYC1 terminator as a terminator for ADH2, and URA3 gene (marker gene) are included.
- FIG. 9 Vector for mhpF gene introduction and ADH2 disruption
- pCR-ADH2U-ERO1_T-mhpF-HOR7_P-URA3-ADH2D shown in FIG. 9 was prepared.
- This vector includes the mhpF gene (same as (7) above) with the HOR7 promoter on the 5 'side and the ERO1 terminator on the 3' side, the region for homologous recombination on the yeast genome and disruption of the ADH2 gene.
- a region of about 700 bp upstream of the ADH2 gene (ADH2U), a region of about 800 bp upstream of the ADH2 gene (ADH2D), and the URA3 gene (marker gene) are included.
- MhpF and ADH1 gene introduction and ADH2 disruption vectors As vectors for mhpF and ADH1 yeast introduction and ADH2 gene disruption, pCR-ADH2U-P_TDH3-ADH1-T_ADH1-ERO1_T-mhpF-HOR7_P- URA3-ADH2D was produced. This vector has the mhpF gene with the HOR7 promoter added at the 5 ′ side and the ERO1 terminator added at the 3 ′ side (same as (7) above), the TDH3 promoter added at the 5 ′ side, and the ADH1 terminator added at the 3 ′ side. ADH1 gene from S.
- ADH2U ADH2 gene
- ADH2D ADH2D gene
- URA3 URA3 gene
- Control vector (marker gene only) As a control vector for introducing only the marker gene, pCR-ADH2part-T_CYC1-URA3-ADH2D shown in FIG. 11 was prepared. This vector contains a region of about 450 bp upstream from the 3 ′ end of the ADH2 gene (ADH2part), a region of about 700 bp downstream from the 3 ′ end (ADH2D), and ADH2 CYC1 terminator and URA3 gene (marker gene) are included as terminators.
- a diploid yeast strain Saccharomyces cerevisiae OC2-T (Saitoh, S. et al., J. Ferment. Bioeng. 1996, Vol. 81, 98-103) was selected on a medium containing 5-fluoroorotic acid (Boeke, JD, et. al. 1987 Methods Enzymol.; 154: 164-75.), and a strain that became uracil-requiring was used as a host.
- Yeast transformation was performed using Frozen-EZ Yeast Transformation II (ZYMO RESEARCH) according to the attached protocol.
- ZYMO RESEARCH Frozen-EZ Yeast Transformation II
- the OC2-T strain was transformed with a fragment obtained by digesting the pUC-HIS3U-P_HOR7-XKS1-T_TDH3-P_TDH2-hph-T_CYC1-HIS3D vector with the restriction enzyme Sse8387I, and applied to a YPD + HYG agar medium.
- the purified colonies were purified.
- the purified selected strain was named OC100 strain.
- pUC-LEU2U-P_HOR7-TAL1-T_TDH3-P_HOR7-TKL1-T_TDH3-HIS3-LEU2D vector was digested with restriction enzyme Sse8387I to transform OC100 strain, and SD agar medium without histidine (Mthods in Yeast Genetics, Cold Spring Harbor Laboratory Press) was applied, and the grown colonies were purified. The purified selected strain was named OC300 strain.
- pUC-GRE3U-P_HOR7-RPE1-T_TDH3-P_HOR7-RKI1-T_TDH3-LEU2-GRE3D vector was digested with restriction enzyme Sse8387I to transform OC300 strain, SD agar medium without leucine The colonies that grew were purified.
- the purified selected strain was named OC600 strain.
- the OC600 strain was transformed with a fragment obtained by digesting the pUC-R67-HOR7p-RsXI-T_TDH3-TRP1d-R45 vector with the restriction enzyme Sse8387I, and applied to an SD agar medium without tryptophan and grown. Colonies were purified.
- the purified selected strain was named OC700 strain. In the OC700 strain prepared as described above, RsXI-C1 gene, XK gene, TAL1 gene, TKL1 gene, RPE1 gene and RKI1 gene are introduced.
- a strain having a high fermentation ability was selected from the strains of Uz1048, Uz1047, Uz928, Uz1012, Uz926, Uz736 and Uz1049 obtained as described above, and a flask fermentation test was performed as follows. First, the test strain was inoculated into a 100 ml baffled flask into which 20 ml of YPD liquid medium (yeast extract 10 g / L, peptone 20 g / L, glucose 20 g / L) with a glucose concentration of 20 g / L was dispensed, and 30 ° C. Culturing was performed at 120 rpm for 24 hours.
- YPD liquid medium yeast extract 10 g / L, peptone 20 g / L, glucose 20 g / L
- the utilization rate of xylose was significantly improved in the Uz736 strain that overexpressed the mhpF gene and ADH1 gene and disrupted the ADH2 gene, as compared to the mhpF overexpressing strain.
- Productivity improved.
- a strain with only ADH2 disruption and a strain with only overexpression of ADH1 did not improve the rate of xylose utilization, so it is considered that there was a synergistic effect.
- the concentration of acetic acid in the medium was significantly decreased, and it was revealed that the acetic acid assimilation ability was also improved.
- Example 2 a recombinant yeast into which a xylose isomerase gene and an mhpF gene of E. coli, an adhE gene, an acetaldehyde dehydrogen gene derived from Clostridium beijerinckii or an acetaldehyde dehydrogen gene derived from Chlamydomonas reinhardtii was prepared.
- a recombinant yeast produced in this example one or both of a pair of endogenous ADH2 genes were disrupted.
- ⁇ Preparation of introduction vector> Plasmid for introduction of XI, XKS1, TKL1, TAL1, RKI1, and RPE1 genes and disruption of GRE3 gene While destroying GRE3 gene at GRE3 locus, 377 of xylose isomerase gene derived from intestinal protists of Reticulitermes speratus The second amino acid was replaced by asparagine to cysteine, and a mutant gene (XI_N337C) with improved xylose utilization rate, a yeast-derived xylulokinase (XKS1) gene, a pentose phosphate circuit transketolase 1 (TKL1) gene, trans A plasmid containing the sequences necessary for introducing aldolase 1 (TAL1) gene, ribulose phosphate epimerase 1 (RPE1) gene and ribose phosphate ketoisomerase (RKI1) gene into yeast, pUC-5U_GRE3-P_HOR7-TKL1-TAL1-
- This plasmid is derived from Saccharomyces cerevisiae BY4742 strain on the 5 'side, TKL1 gene with HOR7 promoter added, TAL1 gene with FBA1 promoter added, RKI1 gene with ADH1 promoter added, RPE1 with TEF1 promoter added Gene, XI_N337C with TDH1 promoter and DIT1 terminator added (fully synthesized sequence with full length converted to codon usage of yeast), XKS1 gene with TDH3 promoter and HIS3 terminator added, on yeast genome
- GRE3U the gene sequence of the region of about 700 bp upstream from the 5 ′ end of the GRE3 gene
- GRE3D the DNA sequence of the region of about 800 bp downstream from the 3 ′ end of the GRE3 gene
- the marker gene is made into
- Each DNA sequence contained in this plasmid can be amplified using the primers shown in Table 2.
- the primer in Table 2 In order to bind each DNA fragment, using the primer in Table 2 with a DNA sequence added so that it overlaps with the adjacent DNA sequence by about 15 bp, template the Saccharomyces cerevisiae BY4742 genome, XI_N337C synthetic gene DNA, and synthetic DNA of LoxP sequence.
- the target DNA fragment was amplified, and the DNA fragments were sequentially bound using In-Fusion HD Cloning Kit (Takara Bio) and the like, and cloned into plasmid pUC19 to prepare the final target plasmid.
- Plasmid for introduction of mhpF / ADH1 gene and disruption of ADH2 gene While disrupting the ADH2 gene at the ADH2 locus E. coli-derived acetaldehyde dehydrogenase gene (mhpF) and yeast-derived alcohol dehydrogenase 1 (ADH1) gene were transformed into yeast.
- a plasmid pUC-5U_ADH2-P_TDH3-ADH1-T_ADH1-DIT1_T-mhpF-HOR7_P-URA3-3U_ADH2 containing a sequence necessary for introduction into the plasmid was prepared.
- This plasmid contains the ADH1 gene with the TDH3 promoter added from the Saccharomyces cerevisiae BY4742 strain on the 5 'side, and the mhpF gene with the HOR7 promoter and DIT1 terminator added.
- a gene sequence (URA3 marker) containing the URA3 gene as a marker.
- Each DNA sequence contained in this plasmid can be amplified using the primers shown in Table 3.
- the target DNA fragment was obtained using Saccharomyces cerevisiae BY4742 genome or mhpF synthetic gene DNA as a template.
- the DNA fragments were sequentially ligated using In-Fusion HD Cloning Ki or the like, and cloned into the plasmid pUC19 to prepare the final target plasmid.
- This plasmid contains the ADH1 gene with the TDH3 promoter added from the Saccharomyces cerevisiae BY4742 strain on the 5 'side, the adhE gene with the HOR7 promoter and DIT1 terminator added (NCBI access No. NP_415757.1, full-length yeast codon A gene sequence (ADH2U) and ADH2 gene 3 in the region of about 700 bp upstream from the 5 'end of the ADH2 gene as a homologous recombination region on the yeast genome. It was constructed so as to include a DNA sequence (ADH2D) of about 800 bp downstream from the side end and a gene sequence containing the URA3 gene as a marker (URA3 ⁇ ⁇ ⁇ ⁇ marker).
- each DNA sequence contained in this plasmid can be amplified using the primers shown in Table 4.
- the plasmid pUC-5U_ADH2-P_TDH3-ADH1-T_ADH1-DIT1_T-mhpF-HOR7_P- was used using a primer in which a DNA sequence was added to the primer of Table 4 so as to overlap with the adjacent DNA sequence by about 15 bp.
- the target DNA fragment was amplified using URA3-3U_ADH2 or adhE synthetic gene DNA as a template, and the DNA fragments were sequentially bound using In-Fusion HD Cloning Kit and cloned into plasmid pUC19 to prepare the final target plasmid.
- This plasmid includes an ADH1 gene derived from the Saccharomyces cerevisiae BY4742 strain on the 5 ′ side and an acetaldehyde dehydrogenase gene derived from Clostridium beijerinckii (NCBI access No.
- YP_001310903.1 A total synthesis of a sequence in which codons are converted in accordance with the codon usage frequency of yeast), and a gene sequence of about 700 bp upstream from the 5 ′ end of the ADH2 gene as a homologous recombination region on the yeast genome ( ADH2U) and a DNA sequence (ADH2D) of about 800 bp downstream from the 3 ′ end of the ADH2 gene, and a gene sequence (URA3URAmarker) containing the URA3 gene as a marker were included.
- each DNA sequence contained in this plasmid can be amplified using the primers shown in Table 5.
- the plasmid pUC-5U_ADH2-P_TDH3-ADH1-T_ADH1-DIT1_T-mhpF-HOR7_P- was used using a primer in which the DNA sequence was added to the primer in Table 5 so as to overlap with the adjacent DNA sequence by about 15 bp.
- a DNA fragment of acetaldehyde dehydrogenated from URA3-3U_ADH2 or Clostridium beijerinckii is used as a template to amplify the desired DNA fragment, sequentially bind the DNA fragment using In-Fusion HD Cloning Kit, etc., and clone to plasmid pUC19 for final purpose
- a plasmid was prepared.
- This plasmid is derived from Saccharomyces cerevisiae BY4742 strain on the 5 'side, ADH1 gene with TDH3 promoter added, acetaldehyde dehydrogenation gene from Chlamydomonas reinhardtii with HIT promoter added and DIT1 terminator (NCBI Access No.
- ADH2U a DNA sequence of about 800 bp downstream from the 3 ′ end of the ADH2 gene, and a gene sequence (URA3 marker) containing the URA3 gene as a marker were included.
- each DNA sequence contained in this plasmid can be amplified using the primers shown in Table 6.
- the plasmid pUC-5U_ADH2-P_TDH3-ADH1-T_ADH1-DIT1_T-mhpF-HOR7_P- was used using a primer in which a DNA sequence was added to the primer of Table 6 so as to overlap with the adjacent DNA sequence by about 15 bp.
- the target DNA fragments are amplified using URA3-3U_ADH2 or Chlamydomonas reinhardtii derived acetaldehyde dehydrogenated synthetic gene DNA as a template.
- the DNA fragments are ligated in sequence using In-Fusion HD Cloning Kit, etc., and cloned into plasmid pUC19.
- a plasmid was prepared.
- mhpF gene introduction plasmid A plasmid containing a sequence necessary for introducing E. coli-derived acetaldehyde dehydrogenation gene (mhpF) into yeast in the vicinity of the ADH2 locus without disrupting the ADH2 gene at the ADH2 locus, pUC-ADH2-T_CYC1 -DIT1_T-mhpF-HOR7_P-URA3-3U_ADH2 was prepared.
- This plasmid is derived from the Saccharomyces cerevisiae BY4742 strain on the 5 'side, and the mhpF gene with the HOR7 promoter and DIT1 terminator added (the total length of the codon converted to match the yeast codon usage)
- the homologous recombination region on the yeast genome includes the ADH2 gene and the DNA sequence of about 800 bp downstream from the 3 'end of the ADH2 gene (ADH2D), and the gene sequence containing the URA3 gene as a marker (URA3 marker) Built in.
- each DNA sequence contained in this plasmid can be amplified using the primers shown in Table 7.
- the plasmid pUC-5U_ADH2-P_TDH3-ADH1-T_ADH1-DIT1_T-mhpF-HOR7_P- was used by using a primer in which the DNA sequence was added to the primer in Table 7 so as to overlap with the adjacent DNA sequence by about 15 bp.
- the target DNA fragment was amplified using URA3-3U_ADH2 or Saccharomyces cerevisiae BY4742 genome as a template, and the DNA fragments were sequentially ligated using In-Fusion HD Cloning Kit, etc., and cloned into plasmid pUC19 to prepare the final target plasmid.
- ⁇ Production of vector-introduced yeast strain The diploid yeast Saccharomyces cerevisiae OC2 strain (NBRC2260) was selected in a medium containing 5-fluoroorotic acid (Boeke, JD, et al. 1987 Methods Enzymol .; 154: 164-75.) And became uracil-requiring.
- the strain (OC2U) was used as a host.
- Yeast transformation was performed using Frozen-EZ Yeast Transformation II (ZYMO RESEARCH) according to the attached protocol.
- the OC2U strain was transformed with a fragment obtained by amplifying the recombination site by PCR, applied to a YPD agar medium containing G418, and the grown colonies were purified. The purified selected strain was named Uz1252.
- This strain was sporulated with a spore formation medium (1% potassium phosphate, 0.1% yeast extract, 0.05% glucose, 2% grape agar) and doubled using homothallic properties.
- a strain was obtained in which the mutant XI gene, TKL1 gene, TAL1 gene, RPE1 gene, RKI1 gene, and XKS1 gene were incorporated into the GRE3 locus region of the diploid chromosome and the GRE3 gene was disrupted. This was designated as Uz1252-3 strain.
- the uracil gene amplified by PCR using the OC2 genome as a template was used to transform the OC2U strain, applied to an SD agar medium without uracil, the grown colonies were purified, and named Uz1313 strain. did.
- the Uz1313 strain was sporulated in a sporulation medium, doubled using homothallic properties, and named Uz1323 strain.
- ⁇ Fermentation test> Two strains each having high fermentation ability were selected from the strains prepared as described above, and a flask fermentation test was performed as follows. First, the test strain was inoculated into a 100 ml baffled flask into which 20 ml of YPD liquid medium (yeast extract 10 g / L, peptone 20 g / L, glucose 20 g / L) with a glucose concentration of 20 g / L was dispensed, and 30 ° C. Culturing was performed at 120 rpm for 24 hours.
- YPD liquid medium yeast extract 10 g / L, peptone 20 g / L, glucose 20 g / L
- D60X80YPAc4 medium (glucose 60 g / L, xylose 80 g / L, yeast extract 10 g / L, peptone 20 g / L, acetic acid 4 g / L) or D40X80YPAc2 medium (glucose 40 g / L, xylose 80 g / L, yeast extra 10 g / L, peptone 20 g / L, acetic acid 2 g / L) were inoculated into a 10 ml flask dispensed with 8 ml, and a fermentation test was performed by shaking culture (80 rpm, amplitude 35 mm, 30 ° C.).
- the stopper attached to the flask was made of rubber with a 1.5 mm inner diameter needle, and a check valve was attached to the tip of the needle so that the flask was kept anaerobically.
- Glucose, xylose and ethanol in the fermentation broth were measured under the following conditions using HPLC (LC-10A; Shimadzu Corporation).
- Tables 9 and 10 show the results of a fermentation test using a D60X80YPAc4 medium with a fermentation time of 66 hours (concentration of charged bacteria: 0.3 g dry cells / L).
- the data shown in Tables 9 and 10 are data average values of three recombinant strains obtained independently.
- Tables 11 and 12 show the results of fermentation tests using D40X80YPAc2 medium with a fermentation time of 42 hours (feeding bacteria concentration 0.24 g dry cells / L), and D40X80YPAc2 medium for hetero-introduced strains.
- Table 13 shows the results of a fermentation test (fermented cell concentration: 0.3 g dry cells / L) when the fermentation time was 42 hours.
- the data shown in Tables 11 to 13 are average data values of three recombinant strains obtained independently.
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Abstract
Description
アセトアルデヒド+NAD++コエンザイムA⇔アセチルコエンザイムA+NADH+H+
0.5グルコース+NADH+H++ATP→グリセリン+NAD++ADP+Pi
アセチルコエンザイムA+NADH+H+→アセトアルデヒド+NAD++コエンザイムA
酢酸+2NADH+2H++ATP→エタノール+NAD++AMP+Pi
(a)配列番号4に示すアミノ酸配列を有するタンパク質
(b)配列番号4に示すアミノ酸配列に対して70%以上の同一性を有するアミノ酸配列を有し、キシロースをキシルロースにする酵素活性を有するタンパク質
(a)配列番号2又は20に示すアミノ酸配列を有する蛋白質
(b)配列番号2又は20に示すアミノ酸配列に対して70%以上の同一性を有するアミノ酸配列を有し、アセトアルデヒド脱水素酵素活性を有する蛋白質
(a)配列番号22に示すアミノ酸配列を有する蛋白質
(b)配列番号22に示すアミノ酸配列に対して70%以上の同一性を有するアミノ酸配列を有し、アセトアルデヒド脱水素酵素活性を有する蛋白質
(a)配列番号24に示すアミノ酸配列を有する蛋白質
(b)配列番号24に示すアミノ酸配列に対して70%以上の同一性を有するアミノ酸配列を有し、アセトアルデヒド脱水素酵素活性を有する蛋白質
本発明に係るエタノールの製造方法に使用される組換え酵母は、キシロースイソメラーゼ遺伝子とアセトアルデヒド脱水素酵素遺伝子とを導入した酵母であって、キシロース代謝能を有する酵母である。ここで、キシロース代謝能を有する酵母とは、本来的にはキシロース代謝能を有しない酵母に対してキシロースイソメラーゼ遺伝子が導入されることによりキシロース代謝能が付与された酵母、本来的にはキシロース代謝能を有しない酵母に対してキシロースイソメラーゼ遺伝子及びその他のキシロース代謝関連遺伝子が導入されることによりキシロース代謝能が付与された酵母、本来的にキシロース代謝能を有する酵母のいずれも含む意味である。
<組換え酵母の作製>
上述したキシロースイソメラーゼ遺伝子及びアセトアルデヒド脱水素酵素遺伝子を宿主となる酵母ゲノムに導入することにより、本発明に使用できる組換え酵母を作製することができる。ここで、キシロースイソメラーゼ遺伝子及びアセトアルデヒド脱水素酵素遺伝子は、キシロース代謝能を有しない酵母に導入しても良いし、キシロース代謝能を本来的に有する酵母に導入しても良いし、キシロース代謝能を有しない酵母にキシロース代謝関連遺伝子とともに導入されても良い。また、キシロースイソメラーゼ遺伝子、アセトアルデヒド脱水素酵素遺伝子及び上述した遺伝子を酵母に導入する際、全ての遺伝子を同時に導入しても良いし、異なる発現ベクターを利用して逐次導入しても良い。
以上で説明した組換え酵母を使用してエタノールを製造する際には、少なくともキシロースを含有する培地にてエタノール発酵培養を行う。すなわち、エタノール発酵を行う培地とは、炭素源として少なくともキシロースを含有することとなる。なお、培地には、予めグルコース等の他の炭素源が含まれていても良い。
本実施例では、キシロースイソメラーゼ遺伝子及び大腸菌のアセトアルデヒド脱水素酵素遺伝子(mhpF遺伝子)を導入した組換え酵母を作製し、この組換え酵母の酢酸代謝能を評価した。
(1)XKS1遺伝子導入用ベクター
S. cerevisiae由来のキシルロキナーゼ(XK)遺伝子の酵母導入用ベクターとして、図1に示すpUC-HIS3U-P_HOR7-XKS1-T_TDH3-P_TDH2-hph-T_CYC1-HIS3Dを作製した。このベクターには、5’側にHOR7プロモーター及び3’側にTDH3ターミネーターが付加されたS. cerevisiae NBRC304 株由来のXK遺伝子であるXKS1遺伝子(genebank:X61377)、酵母ゲノム上への相同組換え領域となるヒスチジン合成酵素(HIS3)遺伝子の上流約500bpの領域(HIS3U)及びその遺伝子内の約500bpの領域(HIS3D)、並びに5’側にTDH2プロモーター及び3’側にCYC1ターミネーターが付加されたハイグロマイシンフォスフォトランスフェラーゼ(hph)遺伝子(マーカー遺伝子)が含まれている。なお、相同組換え領域の外側には制限酵素Sse8387Iのサイトを導入した。また、S. cerevisiae NBRC304 株由来XKS1遺伝子のコーディング領域の塩基配列及び当該遺伝子がコードするキシルロキナーゼのアミノ酸配列をそれぞれ配列番号9及び10に示した。
ヤマトシロアリ(Reticulitermes speratus)腸内原生生物由来のキシロースイソメラーゼ(RsXI-C1、特開2011-147445参照)遺伝子の酵母導入用ベクターとして、図2に示すpUC-R67-HOR7p-RsXI-T_TDH3-TRP1d-R45を作製した。このベクターには、5’側にHOR7プロモーター及び3’側にTDH3ターミネーターが付加されたRsXI-C1遺伝子、酵母ゲノム上への相同組換え領域となるrRNA遺伝子(rDNA)との相同配列であるR45及びR67、並びにプロモーター部分を欠失して発現量を低下させたTRP1dマーカー遺伝子が含まれている。なお、相同組換え領域の外側には制限酵素Sse8387Iのサイトを導入した。R45及びR67により、RsXI-C1を含む遺伝子が第12番染色体上のrDNA座に多コピー導入される。さらにTRP1dマーカーは多コピーで染色体上に導入された場合にはじめてマーカーとして機能する。よって、本ベクターを利用することによって、多コピー導入が可能となる。なお、本実施例においてRsXI-C1遺伝子は、全領域を酵母のコドン使用頻度に合わせて使用するコドンを変換した塩基配列を設計し、その塩基配列に基づいて全合成したものを使用した。本実施例で設計したRsXI-C1遺伝子の塩基配列及び当該遺伝子がコードするキシロースイソメラーゼのアミノ酸配列をそれぞれ配列番号3及び4に示した。
S. cerevisiae由来のトランスアルドラーゼ1(TAL1)遺伝子及びトランスケトラーゼ1(TKL1)遺伝子の酵母導入用ベクターとして、図3に示すpUC-LEU2U-P_HOR7-TAL1-T_TDH3-P_HOR7-TKL1-T_TDH3-HIS3-LEU2Dを作製した。このベクターには、5’側にHOR7プロモーター及び3’側にTDH3ターミネーターが付加されたS. cerevisiae S288 株由来のTAL1遺伝子であるTAL1遺伝子(genebank:U19102);5’側にHOR7プロモーター及び3’側にTDH3ターミネーターが付加されたS. cerevisiae S288 株由来のTKL1遺伝子であるTKL1遺伝子(genebank:X73224);酵母ゲノム上への相同組換え領域となるロイシン合成酵素(LEU2)遺伝子3’側末端より上流約500bpの領域(LEU2U)及びその遺伝子5’側末端上流の約450bpの領域(LEU2D);並びにヒスチジン合成酵素(HIS3)遺伝子(マーカー遺伝子)が含まれている。なお、相同組換え領域の外側には制限酵素Sse8387Iのサイトを導入した。また、S. cerevisiae S288 株由来TAL1遺伝子のコーディング領域の塩基配列及び当該遺伝子がコードするトランスアルドラーゼ1のアミノ酸配列をそれぞれ配列番号11及び12に示した。さらにS. cerevisiae S288 株由来TKL1遺伝子のコーディング領域の塩基配列及び当該遺伝子がコードするトランスケトラーゼ1のアミノ酸配列をそれぞれ配列番号13及び14に示した。
S. cerevisiae由来のリブロースリン酸エピメラーゼ1(RPE1)遺伝子及びリボースリン酸ケトイソメラーゼ(RKI1)遺伝子の酵母導入用ベクターとして、図4に示すpUC-GRE3U-P_HOR7-RPE1-T_TDH3-P_HOR7-RKI1-T_TDH3-LEU2-GRE3Dを作製した。このベクターには、5’側にHOR7プロモーター及び3’側にTDH3ターミネーターが付加されたS. cerevisiae S288 株由来のRPE1遺伝子であるRPE1遺伝子(genebank:X83571);5’側にHOR7プロモーター及び3’側にTDH3ターミネーターが付加されたS. cerevisiae S288 株由来のRKI1遺伝子(genebank:Z75003);酵母ゲノム上への相同組換え及びアルドースレダクターゼ3(GRE3)遺伝子を破壊するための領域となるGRE3遺伝子の3’末端領域約500bpを含む約800bpの領域(GRE3U)及びGRE3遺伝子の上流約1000bpの領域(GRE3D);並びにロイシン合成酵素(LEU2)遺伝子(マーカー遺伝子)が含まれている。なお、相同組換え領域の外側には制限酵素Sse8387Iのサイトを導入した。また、S. cerevisiae S288 株由来RPE1遺伝子のコーディング領域の塩基配列及び当該遺伝子がコードするリブロースリン酸エピメラーゼ1のアミノ酸配列をそれぞれ配列番号15及び16に示した。さらに、S. cerevisiae S288株由来RKI1遺伝子のコーディング領域の塩基配列及び当該遺伝子がコードするリボースリン酸ケトイソメラーゼのアミノ酸配列をそれぞれ配列番号17及び18に示した。
宿主に内在するADH2遺伝子の破壊用ベクターとして、図5に示すpCR-ADH2U-URA3-ADH2Dを作製した。このベクターには、酵母ゲノム上への相同組換え及びアルコールデヒドロゲナーゼ2(ADH2)遺伝子を破壊するための領域として、ADH2遺伝子の上流約700bpの領域(ADH2U)、ADH2遺伝子の下流約800bpの領域(ADH2D)、並びにオロチジン-5’-リン酸デカルボキシラーゼ(URA3)遺伝子(マーカー遺伝子)が含まれている。
アルコールデヒドロゲナーゼ1(ADH1)遺伝子の酵母導入用ベクターとして、図6に示すpCR-ADH2part-T_CYC1-P_TDH3-ADH1-T_ADH1-URA3-ADH2Dを作製した。このベクターには、5’側にTDH3プロモーター及び3’側にADH1ターミネーターが付加されたS. cerevisiae S288 株由来のADH1遺伝子(genebank:Z74828.1)、酵母ゲノム上への相同組換え領域となるADH2遺伝子の3’側末端より上流約450bpの領域(ADH2part)及び3’側末端より下流の約700bpの領域(ADH2D)、ADH2のターミネーターとしてCYC1ターミネーター、並びにURA3遺伝子(マーカー遺伝子)が含まれている。
E. coli由来のアセトアルデヒド脱水素酵素(mhpF)遺伝子の酵母導入用ベクターとして、図7に示すpCR-ADH2part-T_CYC1-ERO1_T-mhpF-HOR7_P-URA3-ADH2Dを作製した。このベクターには、5’側にHOR7プロモーター及び3’側にERO1ターミネーターが付加されたE. coli由来のアセトアルデヒド脱水素遺伝子(mhpF遺伝子)、酵母ゲノム上への相同組換え領域となるADH2遺伝子の3’側末端より上流約450bpの領域(ADH2part)及び3’側末端より下流の約700bpの領域(ADH2D)、ADH2のターミネーターとしてCYC1ターミネーター、並びにURA3遺伝子を含む遺伝子(マーカー遺伝子)が含まれている。なお、本実施例においてmhpF遺伝子は、全領域を酵母のコドン使用頻度に合わせて使用コドンを変換した塩基配列を設計し、その塩基配列に基づいて全合成したものを使用した。本実施例で設計したmhpF遺伝子の塩基配列及び当該遺伝子がコードするアセトアルデヒド脱水素酵素のアミノ酸配列をそれぞれ配列番号1及び2に示した。
mhpF遺伝子及びADH1遺伝子の酵母導入用ベクターとして、図8に示すpCR-ADH2part-T_CYC1-P_TDH3-ADH1-T_ADH1-ERO1_T-mhpF-HOR7_P-URA3-ADH2Dを作製した。このベクターには、5’側にHOR7プロモーター及び3’側にERO1ターミネーターが付加されたmhpF遺伝子(上記(7)と同じ)、5’側にTDH3プロモーター及び3’側にADH1ターミネーターが付加されたS. cerevisiae S288 株由来のADH1遺伝子(上記(6)と同じ)、酵母ゲノム上への相同組換え領域となるADH2遺伝子の3’側末端より上流約450bpの領域(ADH2part)、及び3’側末端より下流の約700bpの領域(ADH2D)、ADH2のターミネーターとしてCYC1ターミネーター、並びにURA3遺伝子(マーカー遺伝子)が含まれている。
mhpF遺伝子の酵母導入及びADH2遺伝子破壊用ベクターとして、図9に示すpCR-ADH2U-ERO1_T-mhpF-HOR7_P-URA3-ADH2Dを作製した。このベクターには、5’側にHOR7プロモーター及び3’側にERO1ターミネーターが付加されたmhpF遺伝子(上記(7)と同じ)、酵母ゲノム上への相同組換え及びADH2遺伝子を破壊するための領域となるADH2遺伝子の上流約700bpの領域(ADH2U)及びADH2遺伝子の上流約800bpの領域(ADH2D)、並びにURA3遺伝子(マーカー遺伝子)が含まれている。
mhpF遺伝子及びADH1遺伝子の酵母導入並びにADH2遺伝子破壊用ベクターとして、図10に示すpCR-ADH2U-P_TDH3-ADH1-T_ADH1-ERO1_T-mhpF-HOR7_P-URA3-ADH2Dを作製した。このベクターには、5’側にHOR7プロモーター及び3’側にERO1ターミネーターが付加されたmhpF遺伝子(上記(7)と同じ)、5’側にTDH3プロモーター及び3’側にADH1ターミネーターが付加されたS. cerevisiae S288 株由来のADH1遺伝子(上記(6)と同じ)、酵母ゲノム上への相同組換え及びADH2遺伝子を破壊するための領域となるADH2遺伝子の上流約700bpの領域(ADH2U)及びADH2遺伝子の上流約800bpの領域(ADH2D)、並びにURA3遺伝子(マーカー遺伝子)が含まれている。
マーカー遺伝子のみ導入するコントロールベクターとして、図11に示すpCR-ADH2part-T_CYC1-URA3-ADH2Dを作製した。このベクターには、酵母ゲノム上への相同組換え領域となるADH2遺伝子の3’側末端より上流約450bpの領域(ADH2part)及び3‘側末端より下流の約700bpの領域(ADH2D)、ADH2のターミネーターとしてCYC1ターミネーター、並びにURA3遺伝子(マーカー遺伝子)が含まれている。
2倍体酵母のSaccharomyces cerevisiae OC2-T株(Saitoh, S.ら、J. Ferment. Bioeng. 1996年、81巻 98-103)を5-フルオロオロチン酸添加培地で選抜し(Boeke, J.D., et al. 1987 Methods Enzymol.;154:164-75.)、ウラシル要求性となった株を宿主とした。
上述のように得られたUz1048、Uz1047、Uz928、Uz1012、Uz926、Uz736及びUz1049系統の株からそれぞれ発酵能力が高い株を選び、フラスコ発酵試験を以下のように実施した。まず、グルコース濃度20g/LのYPD液体培地(イーストエキストラクト 10g/L、ペプトン 20g/L、グルコース 20g/L)を20ml分注した100ml容バッフル付きフラスコに供試株を植菌し、30℃ 120rpmで24時間培養を行った。集菌後、D20X60YAc6培地(グルコース20g/L、キシロース60g/L、イーストエキストラクト10g/L、酢酸6g/L)を10ml分注した20ml容フラスコに植菌し(菌濃度0.3g乾燥菌体/L)、振盪培養(80rpm、振幅35mm、30℃)にて発酵試験を行った。なお、フラスコにつける栓は、内径1.5mmニードルを通したゴム製で、ニードルの先に逆止弁を取り付けることでフラスコが嫌気的に保たれるようにした。
移動相:0.01N H2SO4
流量:0.6ml/min
温度:30℃
検出器:示差屈折率検出器 RID-10A
<発酵試験結果>
上記発酵試験の結果を表1に示す。
本実施例では、キシロースイソメラーゼ遺伝子及び大腸菌のmhpF遺伝子、adhE遺伝子、Clostridium beijerinckii由来のアセトアルデヒド脱水素遺伝子又はChlamydomonas reinhardtii由来のアセトアルデヒド脱水素遺伝子を導入した組換え酵母を作製した。本実施例で作製した組換え酵母では、内在する一対のADH2遺伝子のうち一方又は両方を破壊した。
(1)XI・XKS1・TKL1・TAL1・RKI1・RPE1遺伝子導入及びGRE3遺伝子破壊用プラスミド
GRE3遺伝子座にGRE3遺伝子を破壊しながら、ヤマトシロアリ(Reticulitermes speratus)腸内原生生物由来のキシロースイソメラーゼ遺伝子の377番目のアミノ酸をアスパラギンからシステインに置換され、キシロースの資化速度が向上した変異遺伝子(XI_N337C)、酵母由来のキシルロキナーゼ(XKS1)遺伝子、ペントースリン酸回路のトランスケトラーゼ1(TKL1)遺伝子、トランスアルドラーゼ1(TAL1)遺伝子、リブロースリン酸エピメラーゼ1(RPE1)遺伝子及びリボースリン酸ケトイソメラーゼ(RKI1)遺伝子を酵母に導入するために必要な配列を含むプラスミド、pUC-5U_GRE3-P_HOR7-TKL1-TAL1-FBA1_P-P_ADH1-RPE1-RKI1-TEF1_P-P_TDH1-XI_N337C-T_DIT1-P_TDH3-XKS1-T_HIS3-LoxP-G418-LoxP-3U_GRE3を作製した。
ADH2遺伝子座にADH2遺伝子を破壊しながら、E. coli由来のアセトアルデヒド脱水素遺伝子(mhpF)及び酵母由来のアルコールデヒドロゲナーゼ1(ADH1)遺伝子を酵母に導入するために必要な配列を含むプラスミド、pUC-5U_ADH2-P_TDH3-ADH1-T_ADH1-DIT1_T-mhpF-HOR7_P-URA3-3U_ADH2を作製した。
ADH2遺伝子座にADH2遺伝子を破壊しながら、E. coli由来のアセトアルデヒド脱水素遺伝子(adhE)及び酵母由来のアルコールデヒドロゲナーゼ1(ADH1)遺伝子を酵母に導入するために必要な配列を含むプラスミド、pUC-5U_ADH2-P_TDH3-ADH1-T_ADH1-DIT1_T-adhE-HOR7_P-URA3-3U_ADH2を作製した。
ADH2遺伝子座にADH2遺伝子を破壊しながら、Clostridium beijerinckii由来のアセトアルデヒド脱水素遺伝子及び酵母由来のアルコールデヒドロゲナーゼ1(ADH1)遺伝子を酵母に導入するために必要な配列を含むプラスミド、pUC-5U_ADH2-P_TDH3-ADH1-T_ADH1-DIT1_T-CloADH-HOR7_P-URA3-3U_ADH2を作製した。
ADH2遺伝子座にADH2遺伝子を破壊しながら、Chlamydomonas reinhardtii由来のアセトアルデヒド脱水素遺伝子及び、酵母由来のアルコールデヒドロゲナーゼ1(ADH1)遺伝子を酵母に導入するために必要な配列を含むプラスミド、pUC-5U_ADH2-P_TDH3-ADH1-T_ADH1-DIT1_T-ChlaADH1-HOR7_P-URA3-3U_ADH2を作製した。
ADH2遺伝子座にADH2遺伝子を破壊せず、ADH2遺伝子座近傍にE. coli由来のアセトアルデヒド脱水素遺伝子(mhpF)を酵母に導入するために必要な配列を含むプラスミド、pUC-ADH2-T_CYC1 -DIT1_T-mhpF-HOR7_P-URA3-3U_ADH2を作製した。
2倍体酵母のSaccharomyces cerevisiae OC2株(NBRC2260)を5-フルオロオロチン酸添加培地で選抜し(Boeke, J.D., et al. 1987 Methods Enzymol.;154:164-75.)、ウラシル要求性となった株(OC2U)を宿主とした。酵母の形質転換は、Frozen-EZ Yeast Transformation II(ZYMO RESEARCH)を用い、添付のプロトコルに従って行った。
上述のように作成した株からそれぞれ発酵能力が高い2株を選び、フラスコ発酵試験を以下のように実施した。まず、グルコース濃度20g/LのYPD液体培地(イーストエキストラクト 10g/L、ペプトン 20g/L、グルコース 20g/L)を20ml分注した100ml容バッフル付きフラスコに供試株を植菌し、30℃ 120rpmで24時間培養を行った。集菌後、D60X80YPAc4培地(グルコース60g/L、キシロース80g/L、イーストエキストラクト10g/L、ペプトン20g/L、酢酸4g/L)又はD40X80YPAc2培地(グルコース40g/L、キシロース80g/L、イーストエキストラクト10g/L、ペプトン20g/L、酢酸2g/L)を8ml分注した10ml容フラスコに植菌し、振盪培養(80rpm、振幅35mm、30℃)にて発酵試験を行った。なお、フラスコにつける栓は、内径1.5mmニードルを通したゴム製で、ニードルの先に逆止弁を取り付けることでフラスコが嫌気的に保たれるようにした。
移動相:0.01N H2SO4
流量:0.6ml/min
温度:30℃
検出器:示差屈折率検出器 RID-10A
<発酵試験結果>
D60X80YPAc4培地を使用して発酵時間を66時間としたときの発酵試験(仕込み菌濃度0.3g乾燥菌体/L)の結果を表9及び10に示す。なお、表9及び10に示すデータは独立して取得した組換え株3株のデータ平均値である。
Claims (14)
- キシロースイソメラーゼ遺伝子とアセトアルデヒド脱水素酵素遺伝子を導入した組換え酵母を、キシロースを含有する培地にて培養してエタノール発酵を行う工程を有するエタノールの製造方法。
- 上記キシロースイソメラーゼ遺伝子は、以下の(a)又は(b)のタンパク質をコードする遺伝子であることを特徴とする請求項1記載のエタノールの製造方法。
(a)配列番号4に示すアミノ酸配列を有するタンパク質
(b)配列番号4に示すアミノ酸配列に対して70%以上の同一性を有するアミノ酸配列を有し、キシロースをキシルロースにする酵素活性を有するタンパク質 - 上記アセトアルデヒド脱水素酵素遺伝子は、大腸菌由来のアセトアルデヒド脱水素酵素をコードすることを特徴とする請求項1記載のエタノールの製造方法。
- 上記大腸菌由来のアセトアルデヒド脱水素酵素は、以下の(a)又は(b)のタンパク質であることを特徴とする請求項3記載のエタノールの製造方法。
(a)配列番号2又は20に示すアミノ酸配列を有する蛋白質
(b)配列番号2又は20に示すアミノ酸配列に対して70%以上の同一性を有するアミノ酸配列を有し、アセトアルデヒド脱水素酵素活性を有する蛋白質 - 上記アセトアルデヒド脱水素酵素遺伝子は、Clostridium beijerinckii由来のアセトアルデヒド脱水素酵素をコードすることを特徴とする請求項1記載のエタノールの製造方法。
- 上記Clostridium beijerinckii由来のアセトアルデヒド脱水素酵素は、以下の(a)又は(b)のタンパク質であることを特徴とする請求項5記載のエタノールの製造方法。
(a)配列番号22に示すアミノ酸配列を有する蛋白質
(b)配列番号22に示すアミノ酸配列に対して70%以上の同一性を有するアミノ酸配列を有し、アセトアルデヒド脱水素酵素活性を有する蛋白質 - 上記アセトアルデヒド脱水素酵素遺伝子は、Chlamydomonas reinhardtii由来のアセトアルデヒド脱水素酵素をコードすることを特徴とする(1)記載のエタノールの製造方法。
- 上記Chlamydomonas reinhardtii由来のアセトアルデヒド脱水素酵素は、以下の(a)又は(b)のタンパク質であることを特徴とする(5)記載のエタノールの製造方法。
(a)配列番号24に示すアミノ酸配列を有する蛋白質
(b)配列番号24に示すアミノ酸配列に対して70%以上の同一性を有するアミノ酸配列を有し、アセトアルデヒド脱水素酵素活性を有する蛋白質 - 上記組換え酵母は、更にキシルロキナーゼ遺伝子が導入されたものであることを特徴とする請求項1記載のエタノールの製造方法。
- 上記組換え酵母は、ペントースリン酸経路における非酸化過程の経路を構成する酵素群から選ばれる酵素をコードする遺伝子が導入されたものであることを特徴とする請求項1記載のエタノールの製造方法。
- ペントースリン酸経路における非酸化過程の経路を構成する酵素群は、リボース-5-リン酸イソメラーゼ、リブロース-5-リン酸-3-エピメラーゼ、トランスケトラーゼ及びトランスアルドラーゼであることを特徴とする請求項10記載のエタノールの製造方法。
- 上記培地はセルロースを含有しており、上記エタノール発酵では、少なくとも上記セルロースの糖化が同時に進行することを特徴とする請求項1記載のエタノールの製造方法。
- 上記組換え酵母は、アセトアルデヒドをエタノールに変換する活性を有するアルコール脱水素酵素遺伝子を高発現することを特徴とする請求項1記載のエタノールの製造方法。
- 上記組換え酵母は、エタノールをアセトアルデヒドに変換する活性を有するアルコール脱水素酵素遺伝子の発現量が低下したものであることを特徴とする請求項1記載のエタノールの製造方法。
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CN114774477A (zh) | 2022-07-22 |
JP2014193152A (ja) | 2014-10-09 |
CN114774477B (zh) | 2024-04-09 |
CA2901974C (en) | 2020-01-14 |
CA2901974A1 (en) | 2014-09-04 |
CN105073990A (zh) | 2015-11-18 |
JP6087854B2 (ja) | 2017-03-01 |
BR112015019777A2 (ja) | 2017-08-22 |
US20160002674A1 (en) | 2016-01-07 |
BR112015019777B1 (pt) | 2022-12-06 |
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